Conventionally, in the filtration of water such as seawater, lake water, river water, water in a water supply, and water in a wastewater system, the filtration of liquid for general industrial use such as cooling water for various devices or process liquid, and the filtration of gas and the like of various untreated materials for use in a chemical plant or the like, various filtration devices have been used for the purpose of trapping and removing fine particles, dust, and the like contained therein.
When a filtration device as mentioned above is operated for filtration for a long period, solid matter, gel, dust, and the like are trapped and accumulated in the filter, so that resistance of the fluid to pass through a filter medium increases, and this makes it difficult to filter target fluid in the end. In order to cope with this problem, for example, a process called “backwashing” is carried out periodically, where fluid is made to pass through the filter in a direction opposite to the flow direction for filtration, to remove trapped substances adhering to the filter in order to recover the filtration performance of the filter. This method, called “backwashing”, is an excellent method capable of reducing filter-passing resistance to approximate it to the initial passing resistance easily without demounting the filter. In particular, in the case of a filtration device provided with a dedicated backwashing channel, it is advantageous in that backwashing can be carried out without interrupting the filtration.
As such a filtration device capable of carrying out “backwashing,” there is a filtration apparatus provided with an untreated water inlet for letting untreated water flow into a filtration tank, and a filtered water outlet for letting filtered water obtained by filtering untreated water using filters flow out. The internal space of the filtration tank is divided by the filters into multiple compartments so that the multiple compartments are arranged alternately as inflow chambers communicating with the untreated water inlet and outflow chambers communicating with the filtered water outlet. A backwash collection pipe having a water collection port is disposed so as to come into surface contact with such a filter from the inside of the inflow chamber, and is provided to be movable on the surface of the filter. A backwash water discharge pipe is connected to the backwash collection pipe and extends to the outside of the filtration tank. The backwash collection pipe receives backwash water passing through the filter from the outflow chamber side and flowing into the water collection port. The backwash water separates, from the filter surface, deposits trapped on the filter surface of the inflow chamber side. The backwash collection pipe receives the separated deposits from the water collection port together with the backwash water, and discharges the deposits and backwash water as backwash discharge water through the backwash water discharge pipe to the outside of the filtration tank (for example, see Patent Document 1).
In this filtration apparatus, since backwash is carried out using the backwash collection pipe that comes into surface contact with the filter, or using the backwash collection pipe together with a brush, a superior washing effect can be obtained. Further, since the water collection pipe backwashes only a portion of the area of the filter surface at a time while moving the portion to be backwashed, filtration can be continued even during backwashing in areas of the filter surface that are not subjected to backwashing, and this has the advantage that the usage efficiency of the filtration device is high.
Further, in this filtration apparatus, the compartments are arranged alternately as the inflow chambers communicating with the untreated water inlet and the outflow chambers communicating with the filtered water outlet to increase filtration area, water collection pipes are arranged back to back to backwash the filters arranged opposite to the inside of each inflow chamber, and a distribution pipe common thereto is provided in an integrated fashion. Accordingly, this filtration apparatus has an advantage that it is possible to obtain a simplified structure.